Small Bowel Obstruction
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Accounts for 80% of cases of intestinal obstruction
Can be partial or complete:
  • About 85% of partial obstruction will resolve with conservative treatment
  •  About 85% of complete obstruction will require surgery


  • Adhesions
  • Herniae
  • Tumours
  • Crohn’s
  • Volvulus
  • Gallstone ileus
  • Intersusception
  • Radiation strictures
  • Ischaemia
  • TB
  • Trichobezoar (hair ball – sometimes psychiatric patients eat their own hair)
  • Phytobezoar (excess of fibre – often caused by the pith of an orange)
  • Atresia
  • Parlaytic ileus


  • Inguinal, femoral, umbilical, paraumbilical
  • Epigastric, spigelian, obturator, lumbar
  • Inscisional


These appear filmly strands of fibrous material

Caecal Carcinoma

This obstructs the ileo-caecal valve and actually obstructs the small intestine. These patients will need surgery. The patient will often be anaemic.


  • Colicky abdominal pain – often felt around the umbilucs
    • Tender abdomen only tends to be present in strangulation (complete obstruction)
  • Dilated loops of bowel may be palpable
  • Vomiting – often provides some pain relief
    • Fermentation of the bowel products can produce a foul vomit (faeculant vomit), but faecal vomiting only occurs with fistulae
  • Abdominal distension – increases as the condition progresses
  • Absolute constipation (absence of flatus and stool) – Late sign
  • Auscultation – high pitched ‘tinkling’ bowel sounds
    • ‘Rushing’ sounds may also be heard, and are particularly associated with peristalsis and cramp pain
  • Shock ± oliguria – may be present in late stage disease, and indicate severe, strangulated obstruction.


  • Obstruction results in the dilation of proximal bowel, and the collapse of distal bowel. The normal secretory and digestive functions of the mucosa become impaired.
  • Strangulated obstruction occurs when the blood supply to the obstructed region becomes impaired. It can lead to ischaemia and gangrene within 6 hours of onset!
  • Strangulated obstruction occurs in 25% of cases of small bowel obstruction
  • Typically venous obstruction occurs before arterial
  • Perforation typically occurs at the ischaemic segment


  • Catheter
  • Analgesia
  • TED stockings
  • NG Tube
  • Erect CXR
  • Abdo x-ray (supine)– look for distended bowel (>5cm – the normal size of the small bowel is 2.5cm)
    • Gas in biliary tree – this is a sign of gallstone ileus. Often, the gallstone has fistulated into the small bowel – usually duodenum.
    • Supine AXR is necessary to get the best view of the gas patterns in the abdomen. When erect, these are more difficult to discern
    • Differentiating small and large bowel loops:
      • Small bowel loops are the width of the lumen
      • Large bowel loops are not the complete width of the lumen
  • Blood tests
    • Full blood count (anaemia? – may be present in caecal carcinoma)
    • U+E’s – Fluid and electrolyte disturbance (particularly with potassium) may be present
    • Amylase
    • Likely raised CRP
  • Laparotomy
    • Is the only definitive diagnostic tool, but obviously should not be undertaken lightly!


  • Resuscitation – IV crystalloid with K+
  • NG tube to aspirate content for ‘decompression’
  • Nil By Mouth
  • Wait until patient is hydrated, and electrolytes are in normal range.
  • If not settling, Perform laparotomy

Indications for surgery

  • Strangulation – Significant abdominal pain, or other features of ischaemic bowel – e.g. raised WCC or serum lactate
  • Obstruction due to adhesion rarely requires surgery – if Hx of no previous surgery, adhesions are rare
  • Closed-loop obstruction – as seen in some cases of large bowel obstruction

Paralytic ileus

  • This is a ‘disordered neuromuscular transmission’ within the myenteric plexus
  • Usually occurs after abdo surgery and handling of the bowel. Normally, the different parts of the bowel take different amounts of time to start working properly again (e.g. peristalsis and digestion):
    • Stomach: up to 24 hours
    • Small bowel <24 hours
    • Large bowel 24-48 hours
    • Longer than this can indicate ileus
  • Can also be caused by intra-abdominal infection, metabolic disorders, or a reflux response to retroperitoneal surgery
  • It is usually treated conservatively, and should resolve within a week
  • When present without obstruction (as in the majority of cases), then it is often painless
  • Although it can be a cause of obstruction, it can also be a diagnosis in its own right. Distinguishing small bowel obstruction and paralytic ileus may be difficult:
    • Both show distended bowel on x-ray
    • Both can present with constipation
    • Bowel sounds are absent in ileus, whilst characteristic in obstruction (depending on the location of the obstruction).


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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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